The present invention relates to vessel or pipeline closures, which selectively enclose and seal an interior portion of a pressure containing vessel or pipeline. More particularly, the methods and systems of this invention relate to closures of the type used on pipeline pig launching and receiving systems, and closures used as access portals for pressurized vessels. The methods and system of this invention may improve safety, closure life expectancy, and functional operation.
A closure allows convenient and routine access to the interior of a pressure vessel or other volumetric device. A threaded pipeline closure, for example, consists primarily of a hub added to a pipeline inlet and a removable door that seals pressure within the pipeline. A pipeline xe2x80x9cpigxe2x80x9d is a device which is commonly placed into a pipeline using a threaded closure. Pipelines are commonly cleaned and inspected by launching a pig into the pipeline and recovering it, sometimes along with accumulated debris, at a receiving point. Closures may thus be used to cap an end of both a pig launcher and a pig receiver.
Closures may be included on other volumetric pressure vessels, such as storage tanks. Such vessels may contain fluid at high pressures ranging from full vacuum to above 3700 psig. Closures of this type typically range in nominal pipe size from 2 to over 60 inches, corresponding with the nominal size of the vessel port or entrance to which they attach. Closures are conventionally made of metallic materials, and are often formed in a closed die forging process.
The two main components of a closure are a hub and a cap. The hub may be secured at one end to the pipeline or other vessel by welding, with threads, or with a flanged connection. The opposite end of the hub may have external/male threads to mate with internal/female threads on the cap. The cap may engage the hub to create a seal. An O-ring or other member is conventionally included on either the hub or the cap to seal the contents of the pipeline or other vessel. Heavier closures may have a hinge or other support member, such as a pivoting swing-arm, to retain the cap in the vicinity of the hub and make it easier to manipulate after being disengaged from the hub.
Prior art closures commonly include external xe2x80x9chammer lugsxe2x80x9d or xe2x80x9cwingsxe2x80x9d on the exterior of the cap, allowing the cap to be tightened or loosened with a hammer. In some cases, the hammer used can be quite large and heavy. Although caps are often constructed of resilient steel or other material, repeated hammer blows may permanently deform the lugs. With continued use, the lugs may fold back or xe2x80x9ccauliflower,xe2x80x9d progressively cold-working and embrittling the material.
Several hazards may result from this hammering process. First, metal fragments may fly from the cap as it is struck. The fragments, traveling at high speeds, can create a health and safety hazard. To reduce this hazard, continuous maintenance may be necessary to remove any sharp edges on the cap. Second, sparks may be generated when the cap is struck. Under certain conditions, such as when operating near flammable materials, sparks may be unacceptable. In these instances, special hammers made of brass, rubber, or other materials may be required. Third, repeated hammering can cause stress cracks or other defects in the cap material and threads. These defects reduce the reliability of the closure and create the possibility of leaking and catastrophic release of pressurized fluids contained in the vessel. Hammers may also be difficult to use in confined areas. Cold climates may exacerbate these problems by making the materials more brittle.
There are also practical problems with lug-type closures. First, they require a hammer or other tools to operate. The hammer may be misplaced, or the proper size tool may not be available when needed. A large hammer can be awkward, such as when multiple closures are being serviced, especially in a confined space. If not tightened properly, the chance is greater the cap will loosen and leak, particularly when exposed to vibrations or physical shocks. Alternatively, a lug-type closure may be over tightened because it is impossible to precisely modulate the force with which the lug is struck with the hammer. If the proper size hammer is not available, there is an increased chance of improper tightening. As discussed above, the hammering process impacts wear and tear to the closure, shortening the life of the device. The above are examples of some of the shortcomings associated with the prior art.
The present invention overcomes the disadvantage of the prior art. An improved closure is provided, eliminating the need to tighten and loosen the closure using a hammer.
This invention provides methods and systems for constructing a closure for a pipeline or vessel which is relatively simple to operate, reliable, and cost effective. The closure of this invention eliminates the need for hammering on lugs to tighten or loosen the closure. The closure may be tightened or loosened by applying a substantially tangential force to a radially outward portion of the cap.
In one embodiment, the system includes a screw action of a crank-arm which selectively applies either a tightening or loosening force, through flexible member to thread or unthread the cap.
It is an object of this invention to provide a user friendly reliable closure requiring minimum maintenance. The optionally lug-free closure may eliminate the need for lug hammering and its detrimental effects.
It is a related object of this invention to provide an improved closure whereby the assembly for tightening and loosening a closure is more safe, reliable, and effective than those provided by existing methods and systems.
It is a feature of this invention that the opening and closing mechanism may be safer by virtue of its ability to prevent the closure from leaking or failing unexpectedly, such as may otherwise occur when a closure with hammer lugs is exposed to vibrations or thermal changes.
Another feature of this invention is to provide a closure which is relatively simple to operate and need not require any additional tools to operate.
Yet another feature of this invention that, by eliminating the need for hammering, the corresponding sparks and/or flying particles associated with hammering may also be eliminated, so that the closure may be used in combustible environments, or at other locations in which sparks and flying particles may be hazardous.
Another feature of the invention is an assembly for tightening and loosening the cap on a hub, with the assembly including a collar supported on an anchor and having internal threads for mating engagement with a threaded rod which passes through the collar. Rotation of either the collar or the threaded rod moves the threaded rod axially with respect to the anchor. A stop engaging member positioned on the threaded rod engages a selected one of a plurality of stops to thread and unthread the cap from the hub. In the preferred embodiment, each of a plurality of stops on the cap is a slot which extends to a periphery of the cap, with the slot including a portion substantially tangential to the periphery of the cap. A thrust bearing may be provided to reduce friction when the collar or the threaded rod is rotated relative to the anchor.
It is an advantage of this invention that, by eliminating the need for hammering, the corresponding work-hardening, stress cracks, plastic deformation, and other detrimental effects may also be significantly reduced or eliminated. A related advantage is that maintenance associated with hammer lugs may be eliminated.
A still further advantage is that the closure may not be substantially more expensive than other closures. Existing closures may also be altered or retrofitted to incorporate this invention.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying figures and drawings.